原因状语从句
比较:because, since, as和for1) because语势最强,用来说明人所不知的原因,回答why提出的.问题。当原因是显而易见的或已为人们所知,就用as或 since。
I didn't go, because I was afraid.
Since /As the weather is so bad, we have to delay our journey.
2) 由because引导的从句如果放在句末,且前面有逗 号,则可以用for来代替。但如果不是说明直接原因,而是多种情况加以推断,就只能用for。
He is absent today, because / for he is ill.
He must be ill
, for he is absent today.